AlOH Research Articles

Dissociative adsorption of water in CaNaA zeolites studied by TG, DRIFTS and 1H and 27Al MAS NMR spectroscopy

Three CaNaA zeolites, in which, respectively, 49%, 65% and 83% of the Na + cations were exchanged with Ca 2+ ions, along with a NaA sample were studied by thermogravimetry, temperature-programmed DRIFT spectroscopy and MAS NMR. Thermogravimetric desorption profiles of the Ca 2+ exchanged zeolites show a low-temperature peak between 423 and 508 K as well as two high-temperatures peaks at 853 and 973 K, which are missing in case of the NaA sample. Three main bands at 3603–3611, 3495–3510 and 3552–3565 cm −1, of which the first two are due to bridging Si–OH–Al groups located in 8- and 6-rings, respectively, whereas the third corresponds to Ca(OH) + groups dominate the DRIFT spectra of zeolite samples exchanged with Ca 2+ ions. The intensity of the band at 3603–3611 cm −1 decreases significantly until it vanishes almost completely at 823 K. A simultaneous decreases of the intensity of the band of Ca(OH) + groups is indicative of a low-temperature dehydroxylation process between these two species. The intensity of the other Si–OH–Al group bands at 3495–3510 cm −1 shows almost no change up to 823 K, thus suggesting that these groups participate in a high-temperature dehydroxylation process. A weak band in the region 3670–3680 cm −1 is attributed to Al–OH groups of extra-framework aluminum species formed during dehydration of the CaNaA zeolites. Peaks at 4.3 and 5.2 ppm in the 1H MAS NMR spectra are assigned to Si–OH–Al groups in 8- and 6-rings, respectively. 27Al MAS NMR spectra show two main peaks at 57.3 and 78.7 ppm, which are due to tetrahedrally coordinated aluminum and calcium alumosilicate groups. A weak signal between 12 and 13 ppm ascribed to octahedrally coordinated aluminum disappears at higher temperatures.

Surface charges and Np(V) sorption on amorphous Al and Fe silicates

Sorption onto Si-rich alteration layers of crystalline minerals and nuclear glasses, and onto amorphous secondary silicates of rocks and soils, are expected to retard the migration of actinides in the near- and far-field of high-level waste repositories. In this work, we present experimental and modeling studies on the effects of silicate structure and bulk chemistry, and of solution chemistry, on charges and adsorption of neptunyl ions at surfaces of synthetic, amorphous or poorly ordered silica, Al silicates and Fe silicates. The Al silicates display similar pH-dependent surface charges characterized by predominant Si–O − sites, and similar surface affinities for neptunyl ions, irrespective to their Si/Al molar ratio (varying from 10 to 4.3). Such experimental features are explained by incorporation of Al atoms in tetrahedral position in the silicate lattice, leading to only trace amounts of high-affinity Al–OH surface groups due to octahedral Al. By contrast, the structure of the Fe silicates ensures the occurrence of high-affinity Fe–OH surface groups, whose concentration is shown by proton adsorption measurements to increase with decreasing of the silicate Si/Fe molar ratio (from 10 to 2.3). Nevertheless, experimental data of the adsorption of neptunyl and electrolyte ions show unexpectedly weak effect of the Si/Fe ratio, and suggest predominant Si–OH surface groups. A possible explanation is that aqueous silicate anions, released by dissolution, adsorb at Fe–OH surface groups and/or precipitate as silica gel coatings, because experimental solutions were found at near-equilibrium with respect to amorphous silica. Therefore, the environmental sorption of Np(V) onto Si-rich, amorphous or poorly ordered Al silicates may primarily depend on pH and silicate-specific surface areas, given the low overall chemical affinity of such phases for dissolved metals. By contrast, the sorption of Np(V) on natural, amorphous or poorly ordered Fe silicates may be a complex function of silicate bulk chemistry and solution chemistry, i.e., of pH and aqueous Si concentrations. Simple conceptual models of the surface chemistry of the Al and Fe silicates are developed here, based on the wealth of experimental data of silicate surface charges. The surface complexation models predict reasonably the effect of solution chemistry on the sorption of neptunyl ions on poorly ordered silicates of various compositions, and can thus be useful in extrapolating neptunyl mobility in many geochemical systems.

FT‐Raman and FT‐IR spectroscopic study of synthetic Mg/Zn/Al‐hydrotalcites

AbstractSynthetic Mg/Zn/Al‐hydrotalcites with atomic ratios of 6:0:2, 4:2:2, 2:4:2 and 0:6:2 were characterized by FT‐Raman and FT‐IR spectroscopy. ‘AlOH’ IR translation modes are observed at 419, 427, 559, 616 and 771 cm−1 with two corresponding Raman bands at 465–477 and 547–553 cm−1. ‘MgOH’ IR translation modes are found at 412, 559 and 616 cm−1 with equivalent Raman bands at 464–477 and 547–553 cm−1. The ‘ZnOH’ IR translation mode is found at 445 cm−1 and the Raman modes around 450 and 495 cm−1. The CO32 − group is identified by the ν1(IR) at 1112 cm−1 and a doublet in the Raman around 1045–1055 and 1060 cm−1. ν2(IR) is observed at 874 cm−1. ν3(IR) is a doublet at 1359 and 1381 cm−1. ν4 is observed in both the IR and Raman spectra around 670 and 695–715 cm−1, respectively. In the OH deformation region, a doublet is observed for ‘AlOH’ at 955 and 1033 cm−1 in the IR spectra. The ‘ZnOH’ IR deformation mode is observed at 1462 cm−1. H2O is characterized by a bending mode at 1632 cm−1 and an H‐bonded interlayer H2O mode at 3266 cm−1 with a Raman band between 3244 and 3271 cm−1. The OH stretching region is characterized by three bands in the Raman spectra around 3355–3360, 3440–3455 and 3535–3580 cm−1. One band is observed in the IR spectra at 3471 cm−1. Copyright © 2004 John Wiley & Sons, Ltd.

English

Water quality trends for an 8 year period were analyzed for two acidic springs draining from a partially flooded underground coal mine, and the composite mine-pool outflow of 10 discharges. Time series analysis was used to separate long-term data trends from short-term noise. Short-term variation usually constituted less than 30 percent of the trend concentration. Exponential functions were fitted to the trend data, and time estimates (t50C) for concentration to decline 50% were generated for Total Acidity, Fe, Al, SO4, Co, Ni, and Zn concentrations. Iron decline is similar at two springs with an estimated t50C of 60 months. Sulfate t50C is about 60 to 70 months at one spring and for the aggregate mine-pool. Cobalt, Ni and Zn declines are more rapid, with estimated t50C of about 30 to 50 months. Aluminum decline is 2 to 3 times slower than rates for other parameters, and mine-waters are near apparent equilibrium for the mineral jurbanite, Al(SO4)OH*5H2O. Constituent fluxes are controlled mostly by flow, and decline with time. Estimated time (t50F) for flux to decline 50% for the composite mine-pool outflow is about 85 months for Fe, 80 months for SO4 and 105 months for acid flux. Fluxes are 1.5 to 3 times greater in spring than fall, and reflect seasonal distribution of precipitation and recharge to the mine. Most of the improvement in mine-pool discharge results from declining pollutant concentrations. These trends suggest a slow decline in pyrite oxidation, with significant water quality improvement occurring on the order of years to decades.

Uranyl sorption by smectites: spectroscopic assessment of thermodynamic modeling.

Batch sorption experiments and thermodynamic modeling of the interaction of UO2(2+) and its hydrolysis products with two smectitic clay minerals, the reference material SWy-1 [McKinley et al., Clays Clay Miner. 43 (1995) 586] and the soil isolate LK-1 [Turner et al., Geochim. Cosmochim. Acta 30 (1996) 3399], have established a conceptual framework for uranyl/smectite surface complexation based on general reactions between aqueous uranyl species and the reactive sites on the mineral surfaces. In this report, we have formulated and spectroscopically tested a set of hypotheses based on this conceptual framework using samples prepared under similar or identical conditions to evaluate the agreement between surface complexation/speciation as enumerated by spectroscopic characterization and that elaborated by the surface complexation model. Both steady-state and time-resolved optical emission spectral data are presented for uranyl on both smectite minerals as well as on the analogue phases SiO2 and Al(OH)3 spanning the pH range from approximately 4 to 8 and the background electrolyte concentrations from approximately 0.001 to 0.1 M. The spectral data enable the explicit identification of an outer-sphere exchange-site population of the hydrated cation [UO2(OH2)5(2+) ] in SWy-1. Spectral data also clearly establish the existence of inner-sphere surface complexes on the analogue phases and on the amphoteric clay crystallite edge sites [aluminol (>Al-OH) and silanol (>Si-OH)]. Based on the spectral characteristics of these uranyl edge-site populations, it is possible to readily infer for the SiO2, Al(OH)3, and SWy-1 samples the evolution in surface speciation with increasing pH to more hydrolyzed uranyl-surface complexes consistent with the conceptual model. The spectral domain characteristics of the edge-site populations on LK-1 with increasing pH suggest that there is no change in the hydrolysis of the uranyl-surface species. However, emission lifetime data are interpreted as indicating a shift in the surface speciation of the same uranyl-surface species from aluminol sites to silanol sites with pH increase. This observation is also consistent with the conceptual framework of the model. Data are also reported for Eu3+/smectite samples to provide additional insight into the exchange site populations. The emission spectra for Eu3+ in the basal-plane exchange sites differs significantly between SWy-1 and LK-1 samples reflecting a difference in the basal plane spacing between these two minerals, but the emission lifetime data suggest that the Eu3+ cation remains fully hydrated in both systems. The overall general description of surface speciation of uranyl on these mineral phases as enumerated by spectroscopy is in good accord with that derived from the conceptual thermodynamic model, lending added confidence to our understanding and descriptions of surface complexation behavior in this complex geochemical system.

Hyperspectral analysis of the ultramafic complex and adjacent lithologies at Mordor, NT, Australia

The Mordor Complex consists of a series of potassic ultramafic rocks which were intruded into Proterozoic felsic gneisses and amphibolite and are overlain by quartzite and unconsolidated deposits. In situ and laboratory 0.4 to 2.5 μm reflectance spectra show Al–OH absorption features caused by absorption in muscovite, kaolinite, and illite/smectite in syenite, granitic gneiss, quartzite and unconsolidated sedimentary deposits, and Fe,Mg–OH features due to phlogopite, biotite, epidote, and hornblende in the mafic and ultramafic rocks. Ferrous-iron absorption positioned near 1.05 μm is most intense in peridotite reflectance spectra. Ferric-iron absorption is intense in most of the felsic lithologies. HyMap data were recorded in 126 narrow bands from 0.43 to 2.5 μm along a 7-km-wide swath with approximately 6-m spatial resolution. Correction of the data to spectral reflectance was accomplished by reference to in situ measurements of an extensive, alluvial plain. Spectral classes for matched filter processing were selected by using the pixel purity index procedure and analysis of in situ and laboratory spectra. Considering the spatial distribution of the resulting 14 classes, some classes were combined, which produced eight classes characterized by Al–OH absorption features, and three Fe,Mg–OH absorption-feature classes. Comparison of the distribution of these 11 spectral classes to a generalized lithologic map of the study area shows that the spectral distinction among the eight Al–OH classes is related to variations in primary lithology, weathering products, and vegetation density. Quartzite is represented in three classes, syenite corresponds to a single scattered class, quartz–muscovite–biotite schist defines a single very coherent class, and unconsolidated sediments are portrayed in four classes. The three mafic-ultramafic classes are distinguished on the basis of generally intense Fe,Mg–OH and ferrous-iron absorption features. A single class represents the main Mordor ultramafic mass. Epidote-bearing rocks define another class, which corresponds to biotite gneiss and, in the southern part of the area, to fracture zones. The third class, which exhibits Al–OH, as well as Fe,Mg–OH features, represents hornblende gneiss and other mafic gneisses. These results indicate the importance of analyzing the VNIR and SWIR spectral shape and albedo, as well as analyzing specific spectral features, for mapping lithologic units in this weathered terrain.

Long-term water quality trends in a partly flooded underground coal mine

Water quality trends for an 8 year period were analyzed for two acidic springs draining from a partially flooded underground coal mine, and the composite mine-pool outflow of 10 discharges. Time series analysis was used to separate long-term data trends from short-term noise. Short-term variation usually constituted less than 30 percent of the trend concentration. Exponential functions were fitted to the trend data, and time estimates (t50C) for concentration to decline 50% were generated for Total Acidity, Fe, Al, SO4, Co, Ni, and Zn concentrations. Iron decline is similar at two springs with an estimated t50C of 60 months. Sulfate t50C is about 60 to 70 months at one spring and for the aggregate mine-pool. Cobalt, Ni and Zn declines are more rapid, with estimated t50C of about 30 to 50 months. Aluminum decline is 2 to 3 times slower than rates for other parameters, and mine-waters are near apparent equilibrium for the mineral jurbanite, Al(SO4)OH*5H2O. Constituent fluxes are controlled mostly by flow, and decline with time. Estimated time (t50F) for flux to decline 50% for the composite mine-pool outflow is about 85 months for Fe, 80 months for SO4 and 105 months for acid flux. Fluxes are 1.5 to 3 times greater in spring than fall, and reflect seasonal distribution of precipitation and recharge to the mine. Most of the improvement in mine-pool discharge results from declining pollutant concentrations. These trends suggest a slow decline in pyrite oxidation, with significant water quality improvement occurring on the order of years to decades.

Spectroscopic characterisation of the strength and stability of the acidic sites of Al-rich microporous micelle-templated silicates

A micelle-templated material with Si/Al=2.5 has been synthesised, then either calcined to provide the H form of the sample or partially exchanged with Li + and Na + ions. After surfactant removal, all samples were microporous, with average diameter around 18 Å. In the H form, sizeable formation of octahedral and pentacoordinated Al was found, whereas, with Na sample, 27Al NMR spectra showed minimal occurrence of octahedral Al, so indicating that Na + cations, in contrast with protons, do compensate tetrahedral Al in the silicate structure. All samples have been characterised via FT-IR spectroscopy of surface hydroxyl species and adsorbed probe molecules acting as Lewis bases (carbon monoxide, ammonia, propene). Although the Si/Al ratio is close to that of Y zeolites, these systems showed definitely weaker acidity, similar to that of amorphous silica–aluminas of low Al content. With H sample, no zeolite-like Brønsted site has been observed, the more acidic hydroxyls being those absorbing at 3660 cm −1, ascribed to SiOAl(OH)OSi groups, able to transfer a proton to ammonia, but not to propene, and undergoing with CO a shift of about 220 cm −1. With Na sample, the nearly complete exchange caused the disappearance of more acidic hydroxyls and of Al 3+ Lewis sites; a fraction of Na + cations resulted not accessible to probe molecules, being probably buried into the thick walls. With Li sample, some AlOH species and Al 3+ Lewis sites are at the surface, as a consequence of the lower degree of exchange.

Scanning electron microscopy and DRIFT study of metal-loaded Y zeolites

The chemical composition of the ‘surface’ of metal-loaded Y zeolites was investigated by SEM technique. The negative correlation between proton C H/Al and metal C Me/Al local concentrations for Mn, Cu and Zn, resulting from the interaction (ion exchange) of metal ions Me 2+ with ‘surface’ hydroxide bridges ≡Al–OH–Si≡ was found. In turn the positive correlation of C H/Al vs. C Me/Al for Cd was explained as stabilization of CdZe 2 and Cd(OH)Ze complexes in the zeolite structure through the formation of hydrogen bonds with hydroxide bridges. The supplementary Diffusive Reflectance Infrared Study of metal-loaded zeolite showed the sensitivity of framework vibration band T–O–T for Me 2+ ions interaction with negative oxygens of zeolite framework. In connection with this finding two groups of ions were recognized: Mn 2+, Cd 2+, Zn 2+ with strong interaction and consequent shift of T–O–T band toward lower frequencies and Co 2+, Ni 2+, Cu 2+ ions group with weak interaction with the zeolite framework with consequent position of T–O–T at higher frequencies.

Aluminum oxide thin films deposited on silicon substrates from Al(NO3)3 and an organic solvent by spray pyrolysis

Aluminum oxide thin films were deposited on silicon substrates at temperatures in the range from 500 to 650 °C, from Al(NO3)3 dissolved in N,N-Dimethylformamide and using the spray pyrolysis technique. The films of aluminum oxide resulted stoichiometric, amorphous and optically transparent in the visible spectrum, with a refractive index close to 1.66 when a 0.2 molar solution of Al(NO3)3 was used. The films as deposited had a surface roughness as low as 3.8 nm and were almost free of Al–OH bonds, depending on the experimental deposition conditions. The best films were incorporated in a Metal–Oxide–Semiconductor structure and were able to stand electric fields up to 2 MV/cm without destructive breakdown and a dielectric constant of 7.95. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis and surface properties of Ti-containing mesoporous aluminophosphates. A comparison with Ti-grafted mesoporous silica Ti-MCM-41

Mesoporous aluminophosphates (ALPO) was synthesised using cetyltrimethylammonium bromide (CTMABr) as a structure-directing agent, phosphoric acid and aluminum sulfate as sources of structure elements. Ti(IV) ions were introduced into mesoporous ALPO by grafting titanocene dichloride, [Cp 2TiCl 2], onto the POH and AlOH groups exposed in the channels. FTIR spectroscopy was used to study surface hydroxyls, and by the use of NH 3 as molecular probe, to assess the surface acidity of both meso-ALPO and meso-Ti-ALPO materials. The coordination of Ti(IV) centres in Ti-ALPO material was studied using DR UV–Vis spectroscopy.

TEABr directed synthesis of ZSM-12 and its NMR characterization

Synthesis of ZSM-12 using tetraethylammonium bromide (TEABr) as the template was investigated. Among the various parameters that affect the crystallization of ZSM-12, aluminum content of the gel, OH −/SiO 2 and TEA/SiO 2 ratios were the important determinants. Systematic variations of these parameters revealed that the TEABr-assisted synthesis had many similarities to the synthesis using TEAOH template reported earlier, with the exception that the OH −/SiO 2 ratios had to be maintained at lower values. Furthermore, the OH −/SiO 2 ratios favorable for ZSM-12 formation lie in a very narrow range. The source of alkalinity also affected the rate of crystallization and the composition of the product. The crystallization was found to be faster and better incorporation of aluminum in the zeolite framework was obtained when NaOH was used to provide alkalinity rather than KOH. Successful synthesis of highly crystalline ZSM-12 samples with Si/Al ratio around 30 was achieved using a minimal amount of relatively inexpensive TEABr (TEA/SiO 2=0.125). Aluminum-27 NMR spectroscopy unambiguously revealed that all aluminum atoms are incorporated in the zeolite framework in tetrahedral coordination. The NMR line-widths of aluminum signals of the calcined samples were significantly larger than those with template incorporated samples. Spin-lattice relaxation times, conventional and rotating frame, as well as magic angle spinning (MAS) cross-polarization data with variable contact time support that there is a significant proton reservoir in the aluminum framework. The NMR data indicate that many distorted tetrahedral sites are formed upon removal of the template and some of these sites contain Al–OH moieties.

Interaction of N2O with Ag+ ion-exchanged zeolites: an FT-IR spectroscopy and quantum chemical ab initio and DFT studies

Abstract FT-IR spectroscopy and theoretical ab initio as well as density functional (DFT) methods have been applied to the investigation of the interaction of N2O with Ag+ counter-cations in a ZSM-5 zeolite. As a preliminary part of the study, the adsorption of N2O on the parent H-Na-ZSM-5 zeolite (from which the Ag-ZSM-5 system was obtained by ion exchange) and the adsorption of CO at low temperature on Ag-ZSM-5, in order to monitor the dispersion of the Ag+ ions, were also performed. It was observed that N2O could be adsorbed on Ag+ counter-cations both N-end and O-end down. The two forms produce distinct bands due to the νNN mode, clearly observable in the 2300–2200 cm−1 range. Conversely, only the νNO band due to the N-end down adduct was observed at 1325 cm−1, the component corresponding to the O-end down form falling below the low frequency limit of IR transparency of the system. Interestingly, the band due to the νNN mode of N2O molecules O-end down adsorbed on Ag+ ions appeared coincident with that of N2O in interaction with AlOH and SiOHAl groups left in the zeolite after exchange with Ag+. However, the former N2O adducts on silver cations appeared to be slightly more stable (less reversible) than the latter adducts.

Composites of Perylene Chromophores and Layered Double Hydroxides: Direct Synthesis, Characterization, and Photo‐ and Chemical Stability

AbstractComposites of the tetra‐anion of the perylene dye N,N′‐di(phenyl‐3,5‐disulfonic acid)perylene‐3,4:9,10‐tetracarboxydiimide (PBITS) with layered double hydroxides (LDHs) were formed by direct synthesis (co‐precipitation at constant pH). The LDHs were of the hydrotalcite (Mg–Al–OH and Zn–Al–OH compositions). During synthesis of the hydrocalumite type (Ca–Al–OH), partial destruction of the dye occurs, being more pronounced at higher pH values. The composites were characterized with regard to their composition by elemental and thermal analysis. From UV‐vis spectroscopic data and powder X‐ray diffraction, a structural model is developed for the composites. In the galleries between the hydroxide layers, the chromophore molecules are stacked in an J‐type arrangement. The compounds have brilliant colors and are insoluble in common solvents. With regard to a possible application as pigments, their photostability and their chemical resistance against a typical application environment was tested. The photostability of the dye molecules and their chemical resistance against setting cement are slightly raised by the occlusion within the LDH structure; however, the photostability of the LDH–cement is lower than that of cement colored with the pure perylene dye.

Use of Dilute Oxalate to Recover Exchangeable Aluminum Immobilized by Sulfate Salt Addition to Rhodic Kandiudult Subsoil

While SO4 salts have been shown to be effective in reducing exchangeable aluminum (Al) and solution Al activity in acidic subsoils, few attempts have been made in the laboratory to recover exchangeable Al immobilized by the suggested mechanisms of Al–OH–SO4 mineral precipitation or co-sorption on sesquioxide surfaces with SO4 and cations added in the salt (salt sorption). Some low-molecular-weight aliphatic acids such as oxalate are well-known for their ability to increase the solubility of Al in soils and oxalate has often been identified as the dominant or one of the dominant organic anions in subsoils. Oxalate is also well-known for its ability to form soluble complexes and a precipitate with calcium (Ca). Therefore, the objective of this study was to investigate the effects of dilute oxalate on the apparent recovery of exchangeable Al immobilized in response to the addition of gypsum (CaSO4·2H2O) and langbeinite (K2SO4·2MgSO4). Following a 6-month equilibration in the laboratory, gypsum and langbeinite added at 15 mmol SO4 kg−1 were equally effective in decreasing exchangeable Al in soil collected from the Bt1 horizon of a Paaloa silty clay (clayey, oxidic, isothermic Rhodic Kandiudult). However, an oxalate loading rate of 16 mmol kg−1 appeared to recover 100% of the exchangeable Al immobilized by langbeinite but only 38% of that immobilized by gypsum. This result was likely due to the formation of an oxalate precipitate or complexes with Ca in the gypsum treatment. It is suggested that the longevity of gypsum effects on reduced exchangeable Al under field conditions may be due in part to the role of Ca in oxalate complexation.

Characterizing cavity-like spaces in active-site models of zeolites

A method for the calculation of fractal surfaces of crystals is presented. The fractal dimension of fragments of zeolites is computed. Results compare well with reference calculations performed with program GEPOL. The active site of Brønsted acid zeolites is modelled by sets of Al–OH–Si units. These units form 2–12-membered rings. Topological indices for the different active-site models are computed. The comparison of calculations performed with programs GEPOL and SURMO2 allows computing the model indices. The cavity-like globularity and rugosity show sharp discontinuities for the ring with 6 units. Most cavity-like spaces show no fractal character. However, the 6–8-ring cavity-like spaces show fractal dimension values lying in the range 4.0–4.3. The 6-unit cavity-like space shows the maximum fractal dimension and is expected to be the most reactive.

On the acid-dealumination of USY zeolite: a solid state NMR investigation

The dealumination of USY (ultrastable Y) zeolites by nitric acid and oxalic acid treatment was systematically investigated by multinuclear solid-state NMR and MQ MAS NMR experiments. The results show that both acids are very effective in removing non-framework Al as well as framework Al but that aluminum is extracted from the lattice at a higher rate by oxalic acid even at low concentrations. The presence of different species (e.g. silanol nest, Al–OH, four-coordinated framework Al, six-coordinated framework Al, six-coordinated non-framework Al and five-coordinated non-framework Al) was detected, and their changes were followed during the dealumination. The investigation gives evidence that the breakdown of the parent USY zeolite mainly depends on the degree of dealumination and that non-framework Al exerts a great effect on the acidity of the USY zeolite. Leaching-induced increase in the Brønsted acidity of the USY zeolite was also observed by 1H MAS NMR spectroscopy. The different distribution of Al species in these samples accounted for the different catalytic performance of n-dodecane cracking.

Angle-resolved x-ray photoelectron spectroscopy of ultrathin Al2O3 films grown by atomic layer deposition

Thin (45 nm) and ultrathin (4.5–1 nm) Al2O3 layers deposited on HF-stripped Si or thin SiO2 surfaces by atomic layer deposition were studied by angle-resolved x-ray photoelectron spectroscopy, before and after rapid thermal annealing (RTA) at 800 °C for 15 min in N2 or annealing in a conventional furnace under ultrahigh vacuum (UHV) (p=10−6 mbar) and N2 at the same temperature. Samples were characterized in terms of chemical defects and interfacial regrowth upon annealing. Chemical defects as Al–OH groups are evidenced from the O 1s spectra even after RTA. Interfacial regrowth, estimated from the Si 2p components intensity, was found (1) to occur upon every kind of annealing, (2) to be dependent on the initial Al2O3 thickness (the thicker the layer the greater the regrowth), and (3) to be significantly reduced on SiO2 surfaces as thin as 0.5 nm. In agreement with previous studies, we also consistently found the presence of an oxidized Si component at the Al2O3/substrate interface centered at 102 eV for which an assignment to silicate groups (Si–O–Al) is proposed, on the basis of other x-ray photoelectron spectroscopy parameters. Given the influence of UHV annealing in interfacial regrowth, Al–OH defects may play an important role in interface oxidation.

Physical properties of selected illites, beidellites and mixed-layer illite–beidellites from southwestern Idaho, and their infrared spectra

The silver–gold ore deposits of the De Lamar mine, the mines in Florida Mountain and the mines in War Eagle Mountain occur in conjunction with large seams of clay minerals, which consist mainly of mixed-layer illite–beidellite. When saturated with groundwater, these clay seams have caused slope failures during mining and processing of ore. The illite–beidellite clays have effective internal friction values, Ø e, as low as 4° and cementation C values of about 1.0 kg f/cm 2. The Fe-beidellite used for the clay core of the mill pond dam has an average Ø e value of 8.3° and C value of 0.79 kg f/cm 2, with an average permeability ( K-value) of 5.6×10 −7 cm/s. The fundamental OH spectra of beidellite, illite and muscovite are similar with beidellite having bands near 3635, 3654 and 3653 cm −1. Montmorillonite has one Al–OH libration band near 915 cm −1, whereas beidellite has a second band near 942 cm −1. In like manner, illites and muscovites have bands from 928 to 933 cm −1, as well as the Al–OH libration bands from 912 to 917 cm −1. The OH libration bands vary both in position and intensity with particle orientation and heating. Combination bands for Fe-bearing muscovite show moderate bands at 4451 cm −1 for ferrous muscovite and at 4471 cm −1 for ferric muscovite. These bands also are present for illites. The dominant Al–OH combination band wave numbers of muscovites form a linear relationship with the Al 2O 3 muscovite contents, but not so precisely for illites. Chemical analysis of illites indicates that the compositions are a continuum into muscovites. Illites from the Miller–Walters mine contain a rather large amount of certain trace elements, whereas the adjacent beidellites do not.

Fractal dimension of zeolite catalysts

Atom—atom analyses of the geometric descriptors, topological indices and fractal dimension D are applied to active-site models of Brønsted acid zeolites. The results are compared with those from the literature for rings and cavities. A method is tested similar to that used in previous works for crystal fragments. The results obtained are encouraging and the good quality of the analysis is clear from a comparison with cavity results. The active sites are modelled by sets of Al—OH—Si units. These bridges form 2–12 membered rings. Indices for the models are calculated. An analysis shows that the maximal Dsi contribution corresponds to the 6-ring, matching the maximal Dcavity. It is suggested that Si plays a main role in the catalytic activity. Most cavities show no fractal character, while for the 6–8 cavities D is the greatest and is a maximum for the 6-cavity, which is expected to be the most reactive. This is in agreement with the greatest flexibility and with the adsorption of ions in the 6-ring reported in the literature. Work is in progress to test the effect of local deformations on the opening and closing of ring apertures and to check the role of Si.